Our working hypothesis states that the pig red cell, lacking glucose metabolism, derives certain metabolic substrate(s) during its transit through the liver or other organs. In this grant period, the possible metabolic substrate isolated from the postnatal pig liver perfusate and hepatocyte extrudate has tentatively been identified as inosine. The first objective is to define and characterize this symbiotic energy metabolism between the non-glycolytic red cells and various organs in more detail as follows: a) Inasmuch as inosine was identified in the livers of the postnatal piglets still having glycolytic red cells, the extent to which the livers of the adult animal may release inosine or other substrate(s) will have to be established; b) in situ prelabelled liver or hepatocytes with or without adenosine deaminase inhibitor will be employed in order to verify whether or not adenosine or adenine can play a substrate role; c) The metabolic apparatus enabling the red cells to depend exclusively upon the nucleoside metabolism will be elucidated with regards to the substrate transport, to the reversibility by the IMP to AMP reaction for the salvage of adenine moiety, and to the efficacy of key enzymes involved in phosphorylation of nucleosides. The second objective of this proposal pertains to the glucose transport which is entirely eliminated, presumably by discarding or inactivating the membrane glucose transporter, during transition from the pig reticulocyte to erythrocyte stage. Recently developed in vitro reconstitution system, allowing the maturation of reticulocytes to erythrocytes will be employed as a model for the identification of glucose transport carriers in particular and for the cellular differentiation in generation. Specifically, the loss of glucose transport accompanying the maturation process will be correlated with the changes in membrane proteins said to be the glucose transporter. Isothiocyanate maltose, an affinity label for glucose transporter, will be used in order to assess its binding properties of membrane proteins. The reactivity of other surface reactive probes and cation ion transport will be elucidated to gain information on the overall structural changes resulting in the cell volume reduction during this cellular transition.